zone 5

Getting back into Brushless Electric and my days in electric were loooong before brushless, and then I spent a long time in Nitro, so I'm a bit confused. I've read lots of what has been posted, and have some questions based on it.

1. What makes a motor/ESC "correct" for 1/10, or 1/8? I understand the KV x volts = RPM, so why would one 3900 motor be okay for 1/8, and one not be? Same for the ESC's? how do you tell if one is okay for 1/8, or if its "only" for 1/10?

2. I have read a lot of posts about overheating the motor/ESC. Some of the answers I read, say that the gearing causes that. What I didn't see, is which way to gear to NOT over heat. Do you gear it down or up? I'm guessing down as that should put less load on the motor but as I said, this is all new so I don't know.

3. On the motor KV ratings, I see people using lower rated motors on 1/8 scale than on 1/10. Wouldn't a higher rated motor get you more speed than the lower? 11.1 x 3900 = 43290 RPM. 11.1 x 2200 = 24420 RPM. I know I'm missing something here, but I hope someone can explain it.

None of my use is racing, 100% bashing around so if an answer is different based on that, let me know.

Thanks a lot. Any input is appreciated. Even if there is a web site out there that I missed that tells me all of this, a link would be great!

bloodpuppy

In not a pro but ill answer what i can.

1/10 scale motors are usually 550 size, which i believe is 55m.. 1/8 scale motors are about 78mm.
Its all about being able to fit in the car/truck.

Gearing is, there are 2 gears, small one on the motor is the pinion, the large one inside the car is the spur. If you have a 20 pinion and a 100 spur you are running at 5 ratio. Usually the higher the better from what i get. If you go lower like a 30/100 you will have a higher top speed / but higher top temps.

usually off road you want a lower KV, like 2-3000 kv if good.
On- road you would want higher.
My friend messed up and has a 5500 kv in a buggy and his car shuts off with heat problems all the time and his batterys swell alot.

Slo-V Flyer

The post above mine is mostly correct. The 1/10th motors are general 540 sized, with some being 550 sized (the motor can is a few millimeters longer) for heavier trucks etc.

Emaxx and Revo, you'd want to use something like an 1/8th scale setup, or a motor at least in the 36x60 or 36x70 mm size range, that means they have a longer rotor and thus can make more torque.

Why use a lower Kv motor in larger scale models? Because they are inherently more torque, inversely to their Kv rating. If given 2 motors of the same size/shape and even brand, a larger and or longer motor, will generally be able to handle MORE amp draw (current) and thus produce more torque (more amps a motor draws, more torque it CAN make).

If a motor is heating up, it means it is overloaded and either you use a smaller pinion, and or larger spur, or you replace it with a lower Kv motor, or maybe if you're way off base, a larger motor. So yes, 90% of the time if your motor is overheating, you want to try a smaller pinion (2-3 teeth lower and test again every 5-6 minutes). SOMETIMES if you gear the motor way too low (too small of a pinion etc) it can heat up also, due to excessive RPMs and other technical reasons, but this is not as common.

If you look at the specs of most brushless motors of varying quality and sizes, you'll notice the larger ones can usually handle more amps than smaller ones.

Hope this helps.

zone 5

This is GREAT info. Thanks Guys!!!!!

On the ESC, can I "assume" that the ones rated to handle higher continuous Amps are the better ones, and the ones that would be used in 1/8? So 200A is better than 50A?


It seems that Lower Kv produces more Tq, so they should be better all the way around. so a 3000 is always going to be better than a 5000? or is there a special purpose for the higher kv motors?

Slo-V Flyer

You use higher Kv motors when you don't want to or are unable to run a high enough voltage.

And yes, more amps an ESC can handle (note: not always the true advertised rating, like everything in life) the better it can handle bigger motors. You may see the Castle Mamba Monster is able to handle 150-200 amps bursts, while a little 1/18th Mamba can only handle 25~ amps.

Lilredmachine

Generally yes, a higher amp rating will be better than a lower one, but it depends on the quality of an esc. For example I would be good money on a 150a hong kong cheapo esc accepting less abuse than a 120a rated esc from a reputable company.

Voltage also has an effect. The higher the voltage rating on an esc, usually the lower the amp rating needs to be/will be. For example a controller rated for 6s or 25v might have a rating of 150a, a similar esc but with a higher voltage rating, say 8s might only be 120a. This is because a higher voltage setup will draw less amps generally so the esc doesn't need to be as robust. So what SLO-V says above is true to a point, in that higher amp esc are better with larger motors, until the motor becomes large enough for the kv to drop below a useable level for the voltage rating of the higher amp rated esc, then voltage rating becomes more important and the amp rating drops away. I've seen eagletree datalogging graphs for a massive LST conversion running a motor that looked like it'd been pulled out of a washing machine on 10s, producing nearly 6hp, but it never peaked over 70 amps to do it. Remember: Higher voltage, lower amps.

High KV motors do have their place. There are situations like in sanctioned race events where competitors will be limited to say a 2s lipo, so have to get the rpm through using a higher KV motor. Infact it is this that has held back brushless for so long, brushless has been around for ages but we are only recently seeing a few HV (high voltage) controllers being released by mainstream companies, and they are only 6s. Racing meant that development centered around getting performance out of small can high kv motors running low voltage which is inefficient. Now we are seeing HV setups flood the market finally. A big can, 1500kv motor running on say 8s lipo is infinitely more powerful and efficient than a 1/10th 9,000kv motor running on 2s, despite the rpm difference.

Slo-V Flyer

Well you are right, however, without proper gearing and or Kv rating, a motor does not automatically draw less amps when fed more volts. As you know, generally the motor will run hotter (due to more amp draw) when run on higher voltage than lower voltage. So in order to run the low kv motor efficiently, you do need to gear it low and or at the correct ratio so it will not pull too many amps.

But anyway that was just a point I wanted to bring up. Go up in voltage, go DOWN in kv rating and probably go down on pinion size (or larger spur gear), to stay more efficient.

zone 5

Thanks a million for the answers!!! Now I at least have the basics down.

bloodpuppy

Dont forgot you have to match batterys with the amp rating and car itself.

3cell batterys use 60A esc , 25A is usually a 2cell, 80A is i believe 4cell. and 150A is a 6cell.

Ifound this out recently. I ordered a 150A and i coulent use my 3s like i wanted, i was planning on wiring them together to make a 6s out of them but that were only producing 105A

Take the MaH of the battery and (multiply) it by the C rating then (divide) by 1000 and that will give you the amps your battery puts out.

EX. My 3s is 3000maH 35C, 3000x35/1000=105A Ineeded 150A Min.

Slo-V Flyer

Actually, you'd probably be OK if you weren't using a crazy big motor or running a big huge truck. It's not the ESC you have to match # to # but more so cover your motor's amp draw, and typically anything over 100-150 amps is more than enough for 1/10th and most 1/8th applications, regardless of if you're running 2-6s lipo. It all depends on how you gear the motor; it may not pull that many amps after all.

rc person 577

1. What the difference is, is the amp rating, 80, 120, 150, 200 1/10 requires a smaller amp rating then 1/8.

2. If you and "over geared" that means your pinion is too big or spur too small. You are exceeding the the amp load on the motor/esc. If you are, gear down.

3. Typically, you run 2s in a 1/10 7.4*3900=28,860rpm, and you run 4s in and 1/8 14.8*32,560rpm

As for batteries the cell count does not count toward the amp rating. So a 2s 5000mah 40c, puts out the same amps as a 6s 5000mah 40c.

However, lilredmachine is right, a higher kv motor on a lower voltage will draw more amps (more heat) then an lower kv on a higher voltage (less heat), basically.

Not quite sure what bloodpuppy is trying to say.

ThunderbirdJunkie

My Feedback: (3)

Just for future reference, running too low of a gear can also overheat the motor, which is what happened to ThunderbirdJunkie's 4600 Castle motor with 18/87 gearing. Pop up to 20/87 and it's happy.

Slo-V Flyer

Yes those Castle motors are very weird, but that is a good point to keep in mind.

acobra

My Feedback: (40)

wires on my ESC are not color coded how do I find out which wire goes where on the motor?

SyCo_VeNoM

Black and red are negative and positive respectively (if you look at the ESC sheet it should have them labeled)

Motor doesn't matter which motor wire you hook up on it. If the RC doesn't go in the direction you want just swap 2. (that goes for brushless and brushed )

acobra

My Feedback: (40)

lalck % red to Batt. I got so the 3 wires going to the motor make no difference so long as the motor turns the right way, correct?

RobbieP

Correct, BL motors do not care what direction they spin. As long as you achieve the correct rotation needed for your applicationyou are good to go.

ThunderbirdJunkie

My Feedback: (3)

Alternatively you could look at the ESC and the motor's solder tabs and just put A to A and B to B and C to C.

acobra

My Feedback: (40)

Thanks, I guess sometimes I can just over think things

Kenny15

Hey Guys, I'm sorta new to this rc stuff so i have a few questions to ask.
First off i was given a nitro rc car with a .25 (4.1cc) nitro engine it is a [tower terror mt rtr] i have used it some and it turns out that a metal piece chiped and scratched up the piston, anyway it turns out that the engine is destroyed so I was thinking of doing an electric conversion. im not very familiar with electric motors and all that. Could someone tell me what kind of motor and esc i would need? i have some 3s li-pos that i would like to use if that is an option. i have a four-wheel drive, 7 pound (no engine or batteries), in between 1/8 and 1/10 scale truck. so im asking what is necessary to get this thing converted to electric (i need a motor and an ESC)
Thanks Guys! ✌

RustyUs

Do you have an electric motor mount?

Kenny15

no but i can either buy one or make one. any suggestions?